1. Field of the Invention
The present invention relates to optical communication, and more particularly, to a method of controlling optical output power in an optical communication system and a passive optical network (PON) system using the method.
2. Description of the Related Art
Fiber To The Home (FTTH) technology is being actively studied and developed all over the world to connect a home to a telephone office using an optical fiber transmission line so as to provide integrated services including voice calls, data services, and broadcasts. The use of FTTH technology will be dramatically increased in the next several years. Particularly, PON systems using FTTH technology are the most common. Recent PON systems include asynchronous transfer mode-passive optical network (ATM-PON), broadband-passive optical network (B-PON), gigabit-passive optical network (G-PON), and Ethernet-passive optical network (E-PON) systems.
Meanwhile, user or subscriber lines or networks should be constructed so as to be able to use the PON systems. For this, transmission lines may be cut when installing new or additional communication nodes or repair existing communication nodes. In this case, users' or operators' eyes and skin can be damaged by optical radiation from the cut portion of the transmission line. Furthermore, even when the transmission line is not cut, such safety problems can occur. That is, when no subscriber, such as an optical network unit (ONU) and an optical network terminator (ONT) (hereinafter, collectively referred to as ONU), accesses the PON system, the same safety problems may occur.
Therefore, proper means or methods should be provided to protect users or operators from optical radiation when an optical communication system operates abnormally due to cut transmission lines or the nonexistence of ONU access. Particularly, protection means or methods are more important for optical communication systems having a high-power light source for providing good transmission characteristics, a number of node connections, long-distance signal transmission, etc.
When a conventional optical system is in an abnormal state, a light source of the system is shut down or is operated at a low output power level to protect users or operators. However, in this case, an additional mechanism or detector is required to detect whether the optical communication system is in an abnormal state, or to detect disconnection of a communication node. Moreover, even when nodes are normally connected to the optical communication system, the optical communication system does not normally operate until the additional mechanism or detector informs the optical communication system of the fact.